1. Technical Field of the Invention
The present invention relates to potentiometers designed to provide voltage selection over a continuous range of voltages. More particularly, the present invention relates to a touch controlled membrane device which provides voltage selection over a continuous range of voltages simultaneously in two or more axis directions of a multi-dimensional field.
2. The Prior Art
Potentiometers for controlling voltage selection are used in numerous types of applications in both home and industry. For example, these devices may be used in the control panels of such things as aircraft and aerospace applications, large construction equipment, computers, lighting systems, arcade games, or kitchen appliances, to name just a few.
In the past the prior art potentiometers for providing voltage selection have typically been of three types. One type provides a manually operated mechanical wiper that is typically controlled by a knob or slider on a control panel. The wiper is always in contact with a resistive element, which provides for voltage selection over a continuous range of voltages. The constant mechanical contact between the wiper and resistive element tends to accelerate the wear and eventual destruction of this type of potentiometer.
A second, more recent type of potentiometer provides an elongated resistive element and an elongated wiper that is parallel to and spaced from the resistive element. See, for example, U.S. Pat. Nos. 3,624,584 and 3,699,492. In this type of potentiometer the elongated wiper is not in constant contact with the resistive element and is used to achieve voltage selection by depressing the wiper at selected locations along its length to bring it into contact with the resistive element, which has a voltage applied to it. Although this type of device reduces wear, it is not possible to produce a continuous range of output voltage levels because the wiper in this type of prior art device is typically segmented. Thus there is some sacrifice in the ability to accurately control voltage selection, which makes the device less versatile.
Recently there has been devised yet another type of potentiometer. See, for example, see U.S. Pat. Nos. 3,895,288 and 3,968,467. This type of device typically includes a continuous length of electrically resistive material, a corresponding continuous length of electrically conductive material which serves as the wiper, and an electrically insulating spacer which serves to simultaneously support and separate the resistive and conductive materials. Either one or both of the resistive and conductive materials are designed as a flexible membrane so that they can be pressed together at any selected location along their length to bring them into electrical contact with each other.
If a voltage is applied across the resistive material a voltage gradient is established along the length of the material. The voltage gradient may be a linear or non-linear function of the material's length depending upon the particular composition of resistive material used. Thus, touching either the top or bottom surface of the flexible membrane will cause the resistive and conductive materials to contact each other, producing a voltage output on the conductive material or wiper. The advantage of this device is that it minimizes wiper contact and reduces wear and yet provides a continuous range of output voltage levels, since the conductive wiper is not segmented.
However, this device, like the other types of prior art potentiometers described above, is limited to a single axis or one dimensional output. And while the single dimensional type prior art potentiometers are extremely practical in applications where it is desirable to provide a voltage representing displacement along a single axis, there are many applications requiring that a control signal represent a discrete position in a two dimensional field. For example, control signals identifying specific locations on a two dimensional field are commonly used in computer graphics, television screens or to remotely control the position of various kinds of antennas or other objects in two dimensions.
One device known in the art which produces a two dimensional or dual axis output is described in U.S. Pat. No. 4,014,217 to Lagasse et al. That device uses a layer of compressible material having an electrical conductivity that varies in accordance with the state of compression of the layer. A matrix of electrodes is distributed on one side of the layer so as to sense current density variations in the layer. By properly comparing the signals produced by the individual electrodes it is possible to determine the approximate point of contact on the layer's surface. While this device provides multiple discrete voltage signals for identifying contact location, it does not provide a single voltage signal which varies continuously as a function of changes in the two dimensional location of contact. Thus, it is relatively complicated in its structure and operation and can define only an approximate position.
A similar type of device used to provide a two dimensional output is described in U.S. Pat. No. 3,440,522 to Kruse. The primary embodiment disclosed in that patent establishes a two dimensional voltage gradient across an area by dividing the area into four quadrants and applying X and Y source voltage levels at multiple peripheral source locations along a circular path surrounding the area. The polarity of each applied X and Y voltage is determined by the quadrant in which the source location is disposed; the magnitude of each applied voltage depends upon the angular position of the source location within the quadrant. Each point in the gradient area has a unique voltage level which can be transferred to a conductive sheet by forcing the sheet into contact with the gradient area at the selected point. This device requires multiple voltage sources or voltage dropping resistors and requires precise circular placement of the source locations in order to establish the desired two dimensional voltage gradient. As a consequence this device is very expensive to manufacture and cannot be used for rectangular field configurations.
Other embodiments described in the Kruse patent utilize numerous separate conductors which are arranged in opposite surfaces so that the location of contact between the surfaces is identified by voltage levels traceable to particular conductors. Thus, only discrete locations corresponding to points of conductor contact may be derived from those embodiments.
In light of the above, it would be an improvement in the art to provide a touch controlled device for providing output voltage selection over a continuous range of voltages simultaneously in two or more axes of a multi-dimensional field such that the output voltage may be representative of any position on that field. It would be a further improvement to provide such a device which utilizes a small number of component parts and is simple and inexpensive to manufacture.